i was driving the other night and all of a sudden everything electrical in my car died. lights, blinkers, windows, etc. The main fuse (attached to the battery) was blown and this is the jl audio fuse for my system. The actual jl audio fuse never blew, but the edge closest to the battery started to melt, and the wire going to the battery started to melt. any ideas or suggestion would be appreciated.
andy

 

Wire/Fuses melt when the power pulled through the wire/fuse is more then the wire/fuse can withstand.

This can be from either a big amp, or a poor electrical connection (or anything else that would impede electron flow. Its possible that the wire wasn't connected firmly to the fuse holder, but its hard to tell in the pictures.

 

Ohm's law states that as resistance goes up current flow drops. The maximum amout of resistance would be an open switch where no current flows, the minimum amount of resistance would be a short circuit where the fuse would blow quite quickly. If a fuse pops "explodes" that it's likely a short. A melted fuse will have just a bit of the fuses metal gone - a small gap - this is likely an overload. A fuse limits current flow in the wires by popping so that the wires don't catch fire.

Where does this fuse sit in the circuits? Didn't you connect the amplifiers directly up to the battery? If not that's the way it has to be.

Replace the fuse once and slowly bring loads back on line. I would leave all the audio off (pull it's fuse) to make sure you don't have an issue with the car itself - run the highbeams, AC, defroster and brake lights. An instant blow is normally a short circuit.

Now replace the fuse to your amplifier and start bringing the volume up. You'll probably find that after awhile the fuse melts which is an indication that you're barely overloading the car's system. Bad thing.

Good luck.

 

However, unfortunately Ohms law doesn't always apply in every application.

The amp is going to try and draw X amount of amps regardless of the situation and effective wire resistance.

If you have a poor connection (typically at a junction) the amp will still try to pull X amount of amps through that connection. If you have a poor connection and try to pull high current through it it will heat up and melt stuff, but it will NOT blow the fuse, as the current is within the tolerable limits. From the picture it looks like the fuse was installed where it was supposed to be installed, withing 18" of the battery.

It is also possible that the wire is just undersized (hard to tell from the picture). If you put a 10ga wire on an amplifier that draws 100amps (with a 100 amp fuse) you will, like stated above, literally catch the wire on fire.

Fun stuff.

 

I forgot to mention that the fuse melted 2 years after the system was installed. And the jl fuse did not blow, or melt in the right spot. The wire connecting to the fuse started to melt, not the actual bridge of the fuse. It was the main fuse for the car that actually blew. When the main fuse was replaced everything worked fine, but i have not tried to put in a new jl fuse and hook up the audio system.

 

Ohms law isn't just a good idea ... it is the law.

Loose connections create I2*R losses and you are right that they will heat up dispating the energy as heat rather than passing the current. The pictures were so blurry I couldn't tell if that was a fuse or a shrimp cocktail.

I2 (current squared) * R (resistance) losses are really important to watch with high current applications like our audio amplifers. Since the current is squared (and some amps are pulling 30 amps of power) a tiny resistance is going to cause high wattage loses. That's why we use big cable with low resistance and gold plated big connectors to get positive connections.

 

PS: Your pictures look like I see without my glasses!

 

What most likely happened is that the insulation melted off of the copper wire, due to heat created by a loose connection. Once the insulation was gone I would guss that the bare wire touched something metal which created a direct short, blowing your main fuse.

Back in the day when I was installing full time we would see quite a few melted fuses under the hood, but generally they were the cheaper, glass fuse holders. They had plastic caps on them that you screwed together and it was supposed to keep everything tight, but over time they would loosen up and the ends would start to separate.

Paul, I still think you are looking too deep in to what I'm describing. A poor connection will still conduct electricity with very little (if any) added resistance. But, once you try to pull 30 amps through a ring connector that is barely hanging on it will create heat, as its pulling more instantanious current through less wire.

Another possibility is that the wire started to corrode, which reduce overall conductivity.

All and all, I would replace the wire and the connectors on the battery side of the fuse and move on!

 

Actually, looking at the right picture you CAN see the blue corrosion. As a wire corrodes it loses its ability to conduct electricity (as current flows on the outside of the wire. Car stereo wire is made up of hundreds of individual strands and as they individuall lose their ability to pass current you are basically left with a smaller wire.

When trying to pull the same amount of current through a smaller (insufficient) wire heat is generated. As the wire heats up the insulation starts to melt off. Once melted off, its only a matter of time till the exposed copper hits something metal and (lucky for you) blew the main fuse. In most cars the amp cable is attached directly to the battery, and if this would happen the car most likely would have went up in flames.

 

here are some better pics

 

will the audio shop that install for you replace a new one?

 

Yeah, definately looks like there is some corrosion going on there!

 

the audio shop that did the install would probably fix it, but i had it installed in New hampshire and i am currently living in South Carolina, and soon to be in Hawaii....